Synthetic resins are materials with comparable properties to natural resins - viscous liquids capable of hardening. They are typically manufactured by esterification or soaping of organic compounds. The classic assortment is epoxy resin, manufactured through polymerization-polyaddition or polycondensation reactions, used as a thermoset polymer for adhesives and composites. One more category, which constitutes the 75 % of resins used, is Unsaturated Polyester Resin. Ion exchange resin is another important class with application in water cleansing and catalysis of organic reactions.